In regards to well-boring operations, there are potentially big challenges in connection with complicated well paths, including deep and long horizontal sections. The need for good hole cleaning is of great significance, as the well drillings of today have hole cleaning problems. Various sludge compositions have been investigated and positive results have been achieved, but an improvement of the sludge composition alone has not been enough to solve the problems. New equipment of different design has also been tested and rotation at different speeds has been tried out in the prior art, without obtaining a reliable improvement of the hole cleaning.
A mechanical flushing device has been developed, which can be mounted in the drill stem or in other stems, such as coil pipes, "snubbing" etc., which are used in connection with well operations. The flushing device can be preadjusted for a desired percentage-wise distribution of the drill sludge, e.g., distribution of supplied drill sludge outwardly through the flushing ports and through the motor/drill head respectively. The flow distribution can be undertaken in a regulatable manner when the flushing device is activated. During drilling, provision is made for drill sludge to be supplied to the motor/drill head.
In the drilling of long wells, which are often complicated with considerable horizontal paths, significant problems have arisen in transporting drill crushings (drill material) to the surface. The development of technology has gone in the direction of higher drilling speed, something which further reinforces the problem.
During normal drilling, the annular space speed for the backward flowing sludge often becomes too slow to whirl up crushings in the annular space. Consequently, the crushings are not suspended to a sufficient degree in the sludge, with the result that the hole cleaning is too poor. The danger of dragging the drill stem along deposited crushings, for example over "stabilizators", increases the chance of packing, wedging, sludge loss, and the like. Furthermore, imperfect hole cleaning generally makes the drilling operations difficult and, by way of example, defective transport of crushings can prevent intentional side displacement ("sliding") by control in horizontal wells, with a reduced drilling speed following from this. Also, it is further known that in elongate wells there are often problems with high moment loadings. Imperfect hole cleaning is a main cause of the problems.
During the drilling operation, the drill sludge is pumped downwards through the drill stem, outwards through the drill head and further backwards through the annular space between the drill stem and the bore hole wall. When the sludge has passed the drill head and is deflected back through the annular space, the speed profile over the hole area will be different. In the horizontal path of the bore hole the drill stem will abut the low side of the bore hole, something which in turn will result in the main flow of sludge following a course into the upper portion of the cross-section of the hole. In the lower portion of the cross-section of the hole, the speed of flow will consequently become significantly lower, something which leads to the crushings being more readily deposited along the flow side of the hole cross-section. Gradually, the flow will become laminar.
By virtue of the above, the drill stem will normally have to be brought upwards from the bottom of the horizontal bore hole portion, in order to attempt to transport the crushings in a direction opposite to the drilling direction. When this is done, a hollow space will arise on the under side of the drill head and the sludge is flushed downwards into the hollow space, in order to be deflected in a direction backwards into the annular space with a subsequent loss of effect. Even with a powerful backward flow of sludge through the annular space, experience dictates that significant amounts of drill crushings are lying behind in the annular space. When introducing pipe linings, and especially when introducing extension pipe ("liner") with associated attachments and with possible associated packings, a little clearance is required. Also, during subsequent cementing, poor cleaning constitutes yet additional problems, such as increased flow resistance, sludge loss and danger of contamination, etc.
A particular aim of the present invention is the application of an inventive flushing arrangement in connection with conventional drilling operations, but in addition, an objective is also to be able to use the flushing arrangement according to the invention in other operations, such as drilling operations in predrilled, pressure-set wells.
With current techniques drill sludge is pumped by means of high pressure pumps located at the surface of the earth, in a powerful current downwards through the drill stem and outwards from the drill head, where the flow of sludge turns and returns back through the annular space whereby the return flow carrying along crushings and transporting the latter in the return flow back to the surface of the earth.
As mentioned, crushings are collected locally in the annular space which is defined between the drill pipe and the wall of the bore hole and blocks the passage through the annular space. A practical solution of the problem has been that the drill stem, after it is drilled a certain length (about 30 m) in the ground formation, is moved axially forwards and backwards in order to contribute thereby to pushing/pressing remaining crushings back through the annular space to the surface of the earth. This pushing/pressing operation is undertaken at the same time as a stream of drilling liquid is pumped downwardly through the drill pipe and outwardly through the drill head. When this pushing/pressing movement is in progress, a hollow space will result between the drill head and the bottom of the bore hole and the drilling liquid. This involves the stream of drilling liquid flowing in a powerful current downwards towards the bottom of the bore hole, in order to be reversed thereafter in the opposite direction in a counterflow against the powerful downwardly directed stream this results in a loss in effect following from this of the drilling liquid which flows further upwards in the annular space around the drill stem. Such forward and backward going movements of the drill pipe, together with the variations in the flows of drilling liquid has produced a certain movement of the crushings, which have had a tendency to be collected locally in the bore hole, but such techniques have been far from satisfactory on use in the extremely long bore holes which are drilled with prevailing techniques.
In U.S. Pat. No. 4,749,044 an arrangement is shown for flushing liquid upwards into an annular space between a drill pipe and the wall of a bore hole, in that a portion of the flow of liquid in the drill pipe is diverted out in the annular space through upwardly directed nozzle openings in the drill pipe, while a second portion of the flow of liquid in the drill pipe is restricted and is led downwards to wards the drill head. There is employed a valve regulatable with the pressure of the flow of liquid. The valve comprises an inner sleeve valve member which is axially moveable internally in the drill pipe in order to cover or uncover the nozzle openings.
In GB 2 192 217 an under member is shown, which is fixed between a drill head and an associated drill stem, which is turned by means of a rotating arrangement arranged at the surface of the earth. Drilling liquid flows from the surface of the earth, through the drill stem via an internal bore in the under member and further via a first set of permanently open nozzles through the drill head towards the bottom of the bore hole. In addition, drilling liquid flows in permanently open branch conduits through the under member, and via a second set of nozzles directly out into an annular space between the under member and the side wall of the bore hole. The second set of nozzles is directed obliquely backwards in the annular space, in order to ensure transport of drill crushings away from the drill head at the inner end of the bore hole and via the annular space in the bore hole back to the surface of the earth.
In U.S. Pat. No. 4,817,739 a pulse generator is proposed for producing a pulsating flushing effect in the annular space between the drill stem and the bore hole. The flushing effect is affected by means of drilling liquid, which is produced in a powerful flow internally through the drill stem to the drill head. From the drill head, a first set of nozzles empties out into the bottom of the bore hole, while from an under member (which is inserted between the drill head and the drill stem just behind the drill head) a second set of nozzles empties out into the annular space between the under member and the bore hole. The second set of nozzles extends in a direction directed obliquely backwards, so that a flushing jet is directed backwards through the annular space. A spring-loaded valve member is adapted to alternately open and close a first passage to the first set of nozzles, while a spring-loaded valve seat member is adapted in an opposite sequence to alternately close and open a second passage to the second set of nozzles. In step with the reciprocating movements of the valve member and the valve seat member internally in the under member, a pulsating flushing effect can be produced in the annular space around the under member.
In U.S. Pat. No. 4,749,044 a separate arrangement is shown for extracting (fishing) of equipment which is left behind in a well bore hole. The separate collecting arrangement is supplied a stream of drilling fluid through the drill stem and further via a central bore through the collecting arrangement. In addition, the collecting arrangement is equipped with a set of nozzle openings directed obliquely backwards, which empty outwards into the annular space between the collecting arrangement and the side wall of the bore hole. The nozzle openings communicate with the central bore via equivalent radial passages through a sleeve-shaped, axially moveable valve member. The valve member is axially moveable internally in the collecting arrangement against the force from a compression spring from a position with a fully open valve to a position with a fully closed valve. The valve member is held by means of the compression spring in a fully open position during downward displacement of the collecting arrangement in the bore hole. Immediately the collecting arrangement is landed on the well hole drilling arrangement left behind in the bore hole the valve member is pushed backwards to the fully closed position against the force from the compression spring.
The blocking problems have constantly increased because the bore holes are drilled constantly for longer periods of time, while at the same time, the paths of the well bore holes are becoming correspondingly complicated.
There are various problems which have to be solved in connection with the backward flow of the return liquid to the surface. This is due to the rheological properties of the drilling liquid, combined with the speed of the return liquid (drilling liquid with drill crushings) in the annular space between drill pipe and drill stem and the sidewall of the bore hole being necessarily relatively low, something which gives an unsatisfactory flow effect when transporting the crushings in the return liquid to the surface.
Recently there has been much investigation on improving the flow conditions of the drill sludge, which generally constitutes the transport fluid (liquid or sludge), which transports the crushings away from the drill head and over/upwards to the surface. At times the problem has been so big that the arrangement has stuck fast in the bore hole based packing of crushings around the drill stem/drill pipe, with significant loss of time, equipment and income following.
On drilling vertical or substantially vertical bore holes in a land-based or ocean-based location ground formation, strings of pipe coupled together in sections have hitherto been employed, which are rotated by drive means from the surface of the earth. In such, connection a technique is employed with which a pull is exerted in the drill stem from the surface so as to relieve portions of the weight loading arising in the drill stem.
In order to be able to utilise the gas or oil deposits which are present in the ground formations optimally and thereby get uncollected larger amounts of these deposits, lateral well bore holes have been made use of in recent years to a steadily increasing degree. In this connection a technique has been put into use, whereby the course of the well bore hole can be allowed to bend from a substantially vertical path to a substantially horizontal path, in order thereafter to continue the bore in the form of a lateral branch bore hole outwards in the ground formation.
In more recent times, where in addition to vertical or substantially vertically extending bore holes the drilling is continued in a horizontal or substantially horizontally extending direction (over to in part large horizontal stretches), a pipe conduit is usually employed, which is coilable on a reel instead of using strings of pipe which can be coupled together in sections. In such a connection, a technique is employed where, in addition to the weight loading of the drill stem, an extra pushing force has been supplied in the coilable pipe conduit in order to propel the drill head in the drilling direction. This technique has involved the drill pipe having a tendency to buckle in a winding course in a horizontal as well as in a vertical plane and to form locally an abutment against the wall of the bore hole on the so-called "low side".
In practice, it has been found that by using coilable pipe conduit, a tendency occurs for blocking by drill crushings particularly on the low side of the drill pipe, something which can cause still greater danger of blocking the transport of the drill crushings in the annular space around the drill pipe.